RPTOR encodes part of a signaling pathway regulating cell growth which responds to nutrient and insulin levels. RPTOR is an evolutionarily conserved protein with multiple roles in the mTOR pathway. The adapter protein and mTOR kinase form a stoichiometric complex. The encoded protein also associates with eukaryotic initiation factor 4E-binding protein-1 and ribosomal protein S6 kinase. It upregulates S6 kinase, the downstream effector ribosomal protein, and it downregulates the mTOR kinase. RPTOR also has a positive role in maintaining cell size and mTOR protein expression. The association of mTOR and RPTOR is stabilized by nutrient deprivation and other conditions which suppress the mTOR pathway. Multiple transcript variants exist for this gene which encode different isoforms.